Telephone system



Qd. 24, 1933. H, H SMITH Er AL 1,932,235

TELEPHONE SYSTEM` Filed July 13, 1931 9 Sheets-Sheet 1 GEN.

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Patented 9ct.. 24, 1933 neue s 'rs es Fics] @als Park, lil., assignors, by mesme assignments, to Associated rElectric Laboratories,

lne., Chicago, lll.,

a corporation ci Delaware.

Application July 13, l93l. Serial No. 550,436

29 Claims.

Y The present invention relates in general to telephone out particularly to toll switching apparatus and equipment for automatic telephone systems.

ln order to increase the revenue derived from long distance toll lines, it is cornn'ion practice to phantom the trunks so 'that tliree talking circuits are available over four conductors and, in addition, to use the individual line conductors for direct current telegraph circuits. In some instances, additional telegraph facilitiesfare provided by employing low frequency alternating current carrier current for telegraph signalling. Where any of these telegraph facilities are provided, it is necessary to employ some type of toll dialling and signalling which will not interfere witn the various 'telegraph circuits and which is incapable of being interfered with by the telegraph signalling currents. I

A system suitable for use in cases where only direct current telegraph circuits are employed is disclosed in the co-penng application of John Wicks, Serial No. 540,:91 filed May 29,

193i, I applicatie that case, low frequency alternating cu impulses of different durations are used for various operating, release, and supervisory signals. However, such a system is not suitable in where alternating current telei 'es are provided. The main object of the present invention is to provide a system of toll dialling and signal- A i may be used on all types of toll lines irrespective of telegraph and other facilities employed. is made possible by the use of signalling current having a frequency lying within the voice frequency range.

ln employing currents of voice frequencies for signalling in telephone systems, the greatest difficulty is encountered in preventing the actual `voice currents from operating the signaling apparatus. According to one feature of the present invention, this difficulty is overcome by ernploying a `casio frequency current lying within voice fr :uency range, and interrupting this asie frequency current at different rates below le frequency to effect the operation of the apparatus.

....ccording to another feature of the invention, w and improved tuned relay is provided only to the basic signalling frequency used wl in turn inte? t the circuit of otliertuned rees relays designed to respond to the various low frequencies at which d to the assignee of the present v frequency current interrupted at the proper low frequencies.

The above and other features of the invention not speciiically mentioned clearly understood from a perusal of the following specifi-cation. when read in connection with the accompanying drawings comprising l to l0, inclusive, whichshows by means of the usual schematicv diagram the application of tne present invention to a multi-office telephone system in which toll connections are completed by the originating toll operator.

In the drawings, Fig. 1 discloses the toll dialling selector TSl in exchange A which terminates one of the inter-ollice trunk lines connecting this exchange with exchange B. Thev toll board inv exchange A is indicated in the upper cord circuit CCl and the dialling cord DCl being merely indicated inthis ligure.

Fig. 2 of the drawings discloses the voice frequency dialling repeater Rl associated with the toll dialling selector TS1. l

Fig. 3 discloses the tone group TG1 associated with the toll dialling selector TS1/and in the lower portion of this-figure is indicated the toll train in exchange A, consisting of the trunk circuitTCl, the toll transmission vselector Sl, and the toll connector C1. The toll transmission selector Sl and the toll connector Cl'rnay be switches of a standard toll train and may be in all respects siroilar to the selector S and connector() disclosed in the patent to Victor S. Tharp, No. 1,811,444, granted June 23, 1931.

Fig. 4 discloses the tone group TG2 associated will be more left-hand portion of the gure, the operatorsV with the toll` dialling selectorTSZ terminating the trunk in exchange B. This tone group is in all respects similar to vthe tone group TG1 in exchange A. A

Figp discloses the tollv dialling selector TS2 located in exchange B and terminating the trunk extending from exchange A. This toll dialling selector is in al1 respects similar to selector TS1 in exchange A. The toll board located in exchange B is indicated in the upper right-hand corner of this figure.

Fig. 6 discloses the voice frequency dialling repeater R2 associated with the toll dialling selector TSZ, and this repeater is inrall respects tone k group TG1.

similar to repeater R1 disclosed in Fig. 2 of the drawings.

An operators cord circuit CC2 and a dialling cord DC2 are shown in the upper` portion of Fig. 7 of the drawings. Only a suiicient portion oi these cord circuits have been disclosed to enable the present invention to be understood. Similar cord circuits are used at each of the toll boards in exchanges A and C. The toll train comprising a trunk circuit TG2, a selector S2, and connector C2, is shown in the lower portion ofthis iigure. The trunk circuit TG2 is the saine as trunk circuit TCl in exchange A, while the selector S2 and connector C2 are theY saine as selector Sl and connector Cl in exchange A, and are preferably of the type disclosed in the above-mentioned patent to Tharp. The toll train shown in the lower portion of this figure is accessible to the toll dialling selector TS2 over conductors 40 to inclusive. In the upper right-hand portion of this drawing, the trunk line extending to exchange C has been indicated and shown as terminating in a toll dialling selector TSS and associated repeater R3 and tone group TG3, and also at the toll board in exchange B atjacks J5 and J6.' The circuits of selector T53, repeater B3, and tone group TG3 are in all respects siniilar to the circuits of the corresponding apparatus disclosed in detail in Figs. l, 2, and 3 of the drawings.` The selector TSS has access to the `saine .toll train as selector TS2, and also has access to Fig. 10 is a trunking layoutof ,the telephone.

systemY including three automatic exchanges, A, B, and C with a toll board located in each exi change. The two-way inter-office trunk lines connecting exchange A with exchange B terminate in the toll board at each exchange and also in voice frequency toll dialling selectors,v such as TS1 in exchange A and TS2 in exchange B. Associated with the toll dialling selector TS1 is the voice frequency dialling repeater R1 and the Similarly, voice frequency dialling repeater vR2 and tone group, TG2 are associated with the toll dialling selector TS2 in lexchange B. Exchanges B and C are interconnected by two-way trunk lines terminating in similar apparatus at each of these exchanges. This gure also discloses the trunking arrangement of the toll train in each of the three cxchanges.

Referring now'to the trunlring layout shown in Fig. l0 of the drawings, a brief description will first be given of the manner in which/the various connections are set up in the system shown. Assuming that the toll operator in ex-i change A receives a request for a connection. to the subscriber T2 in exchange B, the operator inserts the calling end ofr her cord circuit and also her dialling cord circuit into the jacks terminating one of the trunk lines extending to ex= change B. It will be assumed that the trunk terminating in the tollselector TS1 and associated repeater and tone group is the trunk. seized. As

soon as the trunk is seized, the voice frequency dialling repeater R1 transmits a calling signal consisting of an uninterrupted impulse of the basic Jrreopiency current. This calling signal pres the equipment in exchange B for an inco ing call. The toll operator at exchange A then dials the telephone number of the desired subscriber. The first series of impulsesv operates the toll dialling selector TS2 in exchange B to the proper level and the selector then rotates to select an idle trunk circuit, ch as TG2, and associated toll transmission selector S2. The second digit of the called member operates the toll transmission selector S2 -to select a toll connector, such C2, the proper hundreds group. The final two digits of the called number operate the connector C2 into engagement with the desired called line. It is to be understood that one or more ltoll selectors may be inserted between the toll transmission selector, such as S1, 52,01 S3, and the toll connector, such as Cl, C2, or C3, depending upon the sii/.es of the various exchanges and the number of digits in the telephone numbers. .Tfhen the connection has been established, the answering and disconnect supervision and the release functions are controlled over the interoflice trunk line by proper signals of the basic frequency current interrupted at different low equencies' as controlled by the voice frequency epeaters Rl and i case the toll operator at exchange A receives a request for a connection to a subscriber, such as subscriber T3 in exchange C, she inserts her cords in the trunk jacks associated with the trunk line extending to exchange B in the same manner as described above. The iirst digit dialled in case would be the digit il, which would operate the toll dialling selector TS2 to the tenth lcvel and the selector then automatically .rotates to selectJ an idle trunk extending to exchange C and the associated toll dialling selector TSS, repeater R3, and tone group TG3. When this trunk is seized, the voice frequency repeater R3 trans mits a calling signal consisting of uninterrupted basic frequency current over the trunk line to exchange C in order to prepare the apparatus in this exchange for an incoming call. The succeeding four digits dialled by the toll operator then operate the toll selector TSA, the toll transmission selector S3, and the toll connector C3 to establish the connection to the desired subscriber. The supervisory and release functions in this case are controlled by repeaters Rl andBA and the signals are repeated through the intermediate exchange B by the voice frequency dialling repeaters R2 and R3 and associated equipment. Connections from the toll board in exchange B to subscribers in exchange A or exchange C are established in the same manner as connections from toll boards in exchange A to a subscriber in exchange B. The toll operator in exchange C establishes connections to subscribers in exchange B inthe saine manner as previously described for connections from the toll operator in exchange A to a subscriber in exchange B. In case the toll operator in exchange C wishes to establish a connection to a subscriber, such as Tl, in exchange A, she selects a trunk line extending to exchange B and dials the digit 9 which operates the toll selector TSS to the ninth level, and it then automatically rotates to select an idle trunk extending to exchange A'and the associated selector, repeater, tone group. The supervisory and release signals in this case are repeated through exchange B by means of the voice irequency dialling repeaters R2 and R3.

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interval of time required for the closure of springs 234 is required for the closure of springs 235. When relay 233 is energized in the above-traced circuit, the weighted springs start to vibrate, and after an interval armature 234 completes its contact with its associated weighted spring. During this interval of time, an impulse of uninterrupted basic frequency signalling current is being transmitted over the trunk line, as will now be explained.

Referring to the tone group TG1 shown in the upper portion of Fig. 3, the vacuum tube 309 and the associated tuned reed device 313 form a tuned reed oscillator such as disclosed and claimed in the application of Laurence J. Lesh, Serial No. 353,283, filed April 8, 1929, and assigned to the assignee of the present application. This cscil` lator is designed to operate at the basic signalling frequency which is being employed in the system. This may conveniently be 1000 cycles per second. In this case the tuned reed 314 is designed so that its natural period of Vibration is 1000 cycles per second. This tuned reed provides the coupling between the two coils 315V and 316 located in the grid and plate circuits of tube 309, respectively. The device is thereby caused to oscillate at a thousand cycles per second in a manner fully described in the above-mentioned Lesh application.

When relay 306 was operated responsive to the operation of relay 225, as previously described, it completed the circuit for relay 300 at armature 307 and its working contact. Relay 300 operates 'and at armatures 302 and 303 and their working contacts it connects a varying potential taken from potential divider 312 located in the plate circuit of the oscillating tube 309 to Ythe grid circuit ofv amplifying tube 310. The potential on the grid of this tube is thereby Varied at one thousand cycles .per second, causing corresponding changes in the plate current through the primary winding of output transformer 319. A

thousand-cycle alternating current is thereby induced in the secondary winding of this output transformer and transmitted over the truck line through armatures 301 and 305 and their respective working contacts, to trunk conductors 20 and `21 extending to exchange B. At armature 304 and its resting contact relay 300 disconnects the thousand-cycle tuned reed relay 322 so that this relay will not be operated at this time.

The length of the calling signal which is transmitted in the above manner responsive to the operation of relay 225 of repeaterR1 is deter- `mined by the time required for the weighted l spring contact 234 to close.

When these springs close, ground from armature 215 of'relay 212 is extended over the contacts 234 to the upper terminal of the winding of relay 225, thereby shunting this winding and causing the relay to release after an interval. Resistance 232 is provided to prevent the short-circuiting of the battery. Relay 225 in releasing opens the circuit of relay 233 at armature 227 and its Working contact. At armature 228 and its working contact it opens its own locking circuit, and at armature 226 and its working contact it removes ground from the vY conductor extending to relay 306 and allows this relay to release. Relay 306, in releasing, at armature 307 and its Working contact opens the circuit of relay 300 and this relay thereupon releases, opening the grid circuit to the amplifying tube 310 and disconnecting the output transformer from the trunk conductors, thereby terminating the callingsignal.

The splash of uninterrupted thousand-cycle current which was transmitted over the trunk line conductors 20 and 21 responsive to the insertion of the plugs P1 and P2 into jacks J 1 and J2, respectively, at the toll board in exchange A, is received at the tone group TG2 in exchange B over conductors 20 and 21, armatures 401 and 405 and their resting contacts, and through condenser 425 and the primary Winding of input transformer 426. vThe current induced'in the secondary winding of transformer 426 is impressed on the grid of tube 410 through theI resting contact of armature 402 and said armature and resistance 41'7 and condenser 418 in multiple. A one-thousand-cycle pulsating'plate current accordingly flows through the primary winding of transformer 419 and the induced current in the secondary winding of this transformerr flows through the Winding of the thousand-cycle tuned reed relay 422 over armature 404 and its resting contact.

The resistance 417 and condenser 418 connected in multiple in the grid circuit of tube 410 have two functions. First, they are provided in order to increase the impedanceof the grid filament circuit which'is in effect bridged across the line through transformer 426. This eliminates the low impedance shunt across the line during conversation. Second, the resistance and condenser serve as an automatic volume control and maintain the output to the tuned reed relay 422 at a practically constant value. When a signal is being received through transformer 426, the Varying potential is impressed on the grid of tube l410 causing corresponding variations in the plate circuit through the windings of relay 422. As4 the grid of the tube becomes positive some of the electrons emitted from the filament are attracted to the grid. The amount of electrons so attracted' is proportional to the value of thev positive potential on the grid. During the negative half cycles of received current these electrons collect on one plate of condenser 418 and tend to leak olf through resistance 417. The effect of the charge on condenser 418 is to oppose the positive potential placed on the gridr of the tube by the received signal.

In case the received signal is of greater strength, the amount of electrons collected on the grid of the tube is increased and the condenser 418 is charged to a higher degree. This increases the opposition to the positive potential being placed on the grid by the incoming signal. As a result, effective strength of the signal is reduced and the output of the tube to the tuned reed relay is practically the same as it was fo-r the weaker signal. Thus, the stronger the incoming signal, the greater the effect of the grid suppressor circuit comprising resistance 417 and condenser 418, and the resultant output of tube 410 is practically the same irrespective of the strength of the incoming signal. The capacity of condenser 418 is much higher than that used in connection with the ordinary detector circuit. One set of values which has been found to be satisfactory is one megohm' for resistance 417 and .01 m. f. for condenser 418.

Relay 422 responds to thousand-cycle current 1' thereby improving the operation of the tuned reed. The Vibrations of the reed operate the armature 424, thereby opening the circuit Which is normally closed from ground at armature 424 and its resting contact, conductor 22, normally closed springs controlled by armature 613, conductor 655, and through the windings of relays 643, 649, and the lower winding of relay 553 in multiple, to battery. IThe tuned reeds associated with relays 643 and 649 are designed to be set into vibration only when the current through the windings ci these relays is interrupted at a particular low frequency. However, when ground is removed from conductor 555, relay 653 releases and at armature 654 and its resting contact completes the circuit for relay culi extending from ground, armature 554 and its resting contact, Working contact of armature 647 and said armature, armature 605 and its resting contact, upper Winding or relay 60.5, to battery.

Relay 650 operates in its lirst step, and at armature 603 and its Working contact closes a locking circuit for itself from ground at the Working Contact of normally operated armature 548 or" `relay 646. At armature 610 and its Working contact it connects ground to conductor 33. When relay 663 again operates at the end of the calling signal, ground is removed from the junction point of the two windings of relay 650 and this relay now operates completely over both of its Windings in series. At armature 605 and its resting contact it opens the initial energizing circuit, and at the Working contact or this armature it prepares the impulsing circuit over conductor 35 to relay 51S of the toll selector TS2. At armature 601 and its resting contact it opens the incoming signalling lead to the tuned reed relays 654 and 550, and at armatures Go2 and 603 it changes the connections so that frequencies F3 and F4 are available for signalling on the incoming call, and cuts oli the high positive potential and frequency which aroused when the repeater is used on an outgoing call. et armature 605 and its Working Contact, relay 500 connects ground to busy conductor 29. Y

The ground connected to conductor 33 at armature 510 and its working contact is extended over the lower Winding o relay 530 oi toll selector Relay 555 operates and at its upper armature it closes contacts 552 'thereby extending the ground from the busy conductor 29 to the test ing circuit for the upper Winding or relay 550 from ground on the lousy conductor 29. At armatures 555 and its Working contact it connects dial tone to the lower trunk conductor to inform the toll operator at exchange A that the equipmentin exchange E is ready to receive dial irnpulses. et armature 595 and its Working contact it short-circuits the condenser 545 which Vis normally connected in the circuit of relay 544 so that this relay may be used for supervision. At armatures 507 and 558, relay 555 prepares circuits which will be explained late t armature 509 and its working contact it supplies ground for various operating and holding circuits, none of which are eective at this time, and at armature 510 and its resting contact it opens a point in the circuit of the release magnet of the switch. The equipment in exchange B is now ready to be operated to establish the desired connection.

Upon hearing the dial tone, the toll operator at the toll board in exchange A proceeds to dial the digits in theV called telephone number, which in this case is assumed to be 3131. After the number has been dialled, the dialling cord DCI may be removed from jack J1 and used in the establishment of other connections. The dialling cord DCI is the same as the dialling cord DC2 disclosed in Fig. 7 of the drawings. YThe dial is arranged so that the impulsing contacts are no1'- inally open or the standard dial may be used in Lination with a relay arrangement so that the operation of the dial will send corresponding ground impulses over the tip of the dialling plug. Responsive to the dialling of the rst digit, three ground impulses are transmitted over the tip plug and jack J2, conductor 15, Winding of relay 350, to battery. Relay 300 accordingly energizes and releases three times, and at each operation of the relay it connects a thousandcycle potential, generated by the oscillator, through armatures 303 and 302 and their Working contacts to the grid oi tube 310. Accordingly, a thousand-cycle current lovvs through the primary Winding of output transformer 319 and is induced in the secondary winding and transmitted over the trunk line conductors 20 and 21 through the working contacts of armatures 301 and 305 and said armatures. Three impulses at the rate of ten impulses per second are thereby transmitted over the Vtrunk line conductors 20 and 21.

The three impulses of thousand-cycle current are received by the tone group TG2 through the input transformer 425 and connected to the grid of tube 410. Accordingly, three impulses of thousand-cycle current are transmitted through transformer 419 to the thousand-cycle tuned reed relay 422. to each impulse and opens the circuit of relays 543, 549, and 663. Relay 663 releases each time its circuit is opened and at armature 664 and its The tuned reed relay 422 respondsv resting contact it connects ground through the operates at the rst impulse and remains operated throughout the impulse train. At armature 520 and its Working contact, relay 518 transmits three ground impulses to the Vertical magnet 5,80

through armature 586` and its resting contact. Accordingly, the toll selector TS2 is operated three vertical steps and the Wipers comev to rest opposite the third level of bank contacts. At armatureY 533 and its resting contact, relay 529 opens the circuit of relay 536, and at the `nor- Vmally closed springs controlled by armature 532 it opens a point in the circuit of the rotary magnet 579. At armature 532 and its Working contact relay 529 connects ground to the upper terminal of the Winding of relay 531 to prevent the operationor" this relay in series With relay 576 when orf-normal springs 584 are closed ontherst vertical step or" the switch. Oil-normal springs 525 which are closed on the first vertical step of the switch prepare a circuit for release magnet 534, orf-normal springs 530 open a point in the operating circuit of relay 521, and oir-normal springs 535 complete circuits for relays 551 and 512. These circuits extend from ground at the .Working contact of armature 509 and said armature, ofi-normal springs 535, and from this point through the normally closed springs controlled by armature 515, through the Winding of relay l512, to battery, and through resting contact of armature 573 and said armature, through the lower winding ci relay 551, to battery.

Relay 512 operates in the above-traced circuit and at armature 513 and its resting contact disconnects dial tone from the lower trunk conductor; gizing circuit, and at the working contact ciC this armature it completes a locking circui for itself dependent upon the ground through armature 509 of relay 599. At armature 516 and its resting contact it disconnects ground through a resistance from the lower talking conductor. Relay 551, in operating, at armature 555 and its working contact prepares a circuit for the upper winding or" relay 547, at armatures 554, 553, and 552 it prepares a locking circuit for itself and an operating circuit for relays 589 and 555.

Relay 576 operates when oi-norznal springs 584 are closed on the first vertical step of the selector. The operating circuit for this relay extends from ground at the working contact of ar mature 509 and said armature, working contact of armature 582 and said armature, resting con- "tact of armature 585 and said armature, or-

normal springs 584, winding of relay 576, to battery. At armature 578 and its working contact, relay 576 prepares a circuit to the rotary magnet ,579 which is open during the first series of im pulses at armature 532 of the slow-to-release relay 529. At armature 577 and its working contact, relay 576 short-circuits the winding of relay 581.

When relay 529 drops back a short interval "after the cessation of the iirst series of impulses,

a circuit'is completed from ground at the working contact of armature 589 and said armature, normally closed springs controlled by armature 532,

v armature 578 and its working contact, winding "of rotary magnet 579, to battery. The rotary magnet energizes and rotates the wipers of the switch into engagement with the irst set of bank contacts in the third level. At the rotary interl rupter springs of the rotary magnet, the circuit '0Ver armature 583 and its resting contact, interrupter springs of the rotary magnet, oil-normal springs 584, winding of relay 576, to battery. This ground is also connected to the upper terminal of the winding of relay 581, thereby keepe ing'this relay shunted to prevent its operation. Relay 576 operates, and at armature 578 and its working Contact again completes the circuit for the rotary magnet. The rotary magnet operates to lstep the wipers of the selector into engagement with the next set oi bank contacts, and at the interruptor springs associated with the magnet opens the circuit of stepping relay 576 which thereupon releases. Relay 576, in releasing, at

-ifarrnature 578 and its working contact opens the circuit to the rotary magnet which releases and again closes its interrupter springs to close the test circuit to the stepping relay 576. This ine teraction between relay 576 the rotary magnet continues until wiper 589 is stepped into en- At armature 515 it opens the initial enertors.

gagernent with a bank contact upon which there is no ground potential. As soon as wiper 589 fails to find ground potential, relay 581 operates in a circuit from ground at the Working contact of armature 509 and said armature, winding of relay 581, interrupter springs of the rotary magnet, ofnormal this armature it prepares an impulsing circuit from armature 529 of relay 518 through the control wiper 590, and at armature 582 and its working Contact it completes a circuit for the upper winding of relay 567.

Relay 567 energizes and at armature 573 and its resting contact opens the circuit of relay 551, at armature 572 and its working contact it prepares a circuit for the upper winding of relay 547, at armatures 569 and 568 it disconnects the QOL generator leads to prevent the possibility of sigv nalling the operator at the toll board in exchange B, at armature 579 and its working contact it connects battery through a resistance to the sleeve of jack J3 at the toll board in exchange B to operate sleeve relay 596, and at armatures 571 and 574 and their working contacts it completes points in the talking conduc- Relay 596 opens the circuit to the calling relay at the toll board to prevent a false calling signal.

It will be assumed that the iirst trunk available to selector TS2 is the trunk comprising conductors 40 to 48, inclusive, and terminating in the trunk circuit TG2 shown in Fig. 7 of the drawings. When relay 567 operated and closed its armatures 571 and 572, a circuit was cornpleted from ground, upper winding of relay 547, working contact of armature 572 and said armature, working contact of armature 555 and said armature (relay 551 being slow to release, and, therefore, remaining energized for a short time after its circuit is opened at armature 573A of relay 567), resting contact of armature 559 and said armature, working contact of armature 571 and said armature, wiper 588 and bank contact 592, conductor 40, armature 761 and its resting contact, upper winding of relay 754, to battery.

Relays 754 and 547 operate in series yin this circuit. At armature 548 and its working contact relay 547 completes a locking circuit for its lower winding from ground at armature 509 of relay 500 and through off-normal springs 535,

and at armature 549 and its working contact polarized relay 769. Relay 749 operates and vat` armature 752 and its working contact completes the locking circuit for relay 754 which was prepared at armature 756 and its working contact. At armature 751 and its working contact it prepares an energizing circuit for the series relay 757, at armature 750 and its working contact it connects' ground to the release trunk conductor 41 to busy the trunk in the banks of all selector swtches, such as TS2 and TSS, and at armature 753 and its Working contact it opens a point in a bridge circuit including relay 771.

The bridging of relay 769 across the outgoing trunk conductors 774 and 775 closes a loop to the toll transmission selector switch S2 and prepares this switch for operation. As previously stated, the toll transmission selector switch S2, and the connector switch C2 may be in all respects similar to the selector S and connector C disclosed in the previously-mentioned patent to Tharp. Y

When the remaining digits of the desired telephone number are dialled by the toll. operator in exchange A, relay 300 responds to the impulses of each digit and at each operation it connects the thousand-cycle current source tothe trunk line conductors 26 and 21. These impulses of thousand-cycle current are received by the tone group TG2 and bring about the release of relay 663 in repeater R2 in the manner previously explained. Each time relay 663 releases in accordanceY with the impulses oi' the remaining digits it connects ground over the working contact of armature 647 and said armature, armature 605 and its Working contact, conductor 35, Winding of relay ,518, to battery. Relay 518 responds to each impulse, and at armature 519 and its resting contact it opens the circuit of the repeating relay 746 in the trunk circuit TG2. At armature 519 and its working contact it completes the circuit ior relay ,529 which energizes and remains energized throughout each impulse series. The operation of relay 529 opens the lower trunk conductor at armature 531 and its resting contact, but has no other eiect at this time.

Each Atime relay 746 deenergizes in response to the impulses of the succeeding digits, it connects ground over armature 751 and its working contact, resting contact of armature 763 and said armature, winding of relay 757, to battery. Relay 757 operates and at armature 758 and its working contact shunts the windings of polarized relay 769 in order to improve the iinpulsing circuit. At armature`747 and its Working contact, repeating relay 746 opens the loop circuit extending to the toll transmission selector switch S2, thereby repeating the impulses to this switch. The selector switch is stepped to the iirst level and automatically rotates over the bank contacts in this level to ind an' idle trunk extending to an idle connector switch, such as C2. The remaining two digits, 3 and 1, in the called telephone number are received in the same Way and repeated vby thetrunk circuit TG2 to operate the connector switch C2 into engagement with the called line.

When the connector C2 is operated into engagement'with an idle subscribers line, the battery, connections to trunk conductors 774l and 775 are reversed in a manner clearly described in the above-mentioned patent to Tharp, and this reversed battery through the polarized relay 769, which is bridged across the trunk conductors, allows it to operate and at armature 779 `'complete a circuit for relay 769. Relay 760 operates and at armature 764 and its working contact completes a locking circuit for itself to ground at armature 772 of relay 771. At armature 763 and its resting contact it opens the circuit of relay 757, at armature 762 and its working contact it connects an additional ground to the release trunk conductor 41, at armature 765 and its working contact it closes a point in the bridge circuit including relay 771, and at armatures 761 and 766 and their working contacts it short-circuits the condensers 767 and 763, respectively. When these condensers are shortcircuited, the battery connections to conductors 774 and 775 at the toll transmission selector S2 are extended over line conductors 40 and 43, bank contacts 592 and 595, wipers 588 land 591, armatures 571 and ,574 and their working contacts,

armatures 559 and 553 and their resting contacts, armature 555 and its resting contact, armature 506 and its Working contact, and through the winding of relay 544 and retard coil 559.

Relay 544 operates in this circuit and vat armature 545 and its working contact completes a circuit extending from ground on the hold conductor 33, working contact ofv armature 507 and said armature, armature 545 and its Working contact, armature 508 and its working contact, armature 540 and its resting contact, upper Winding of relay ,551, through the resistance to battery. Relay 551 operates, and at armature 554 and its working contact extends the ground through the normally closed contacts controlled by armature 541, winding oi relay 539, to battery. At armature 552 and its Working contact it extends the operating ground for relay 539 to its own upper winding to lock itself energized, and at armature 553 and its working contact it extends this ground to the lower winding of relay 556. Relay 539, in operating, at armature 541 and its working contact completes a locking circuit for itself from ground at armature 509 of relay 500. This ground is also extended over` armature 552 and its working contact, through the upper Winding Aof relay 5.51, and` over the Working contact of armature 553 and said armature, through the lower winding of relay 556. At

armature 540 and its resting contact relay 539 f opens the initial energizing circuit of relay 551 and at the workingl contact of this armature it completes a circuit from ground on the hold conductor 33, Working contact of armature 567 and said armature, armature 545 and its working contact, armature 508 and its working contact, armature 540 and its working contact, conductor 34, resting contact of armature 631 and said armature, lower and upperr windings of relay 618, to battery. The operation of relay 618 brings about the transmission of a supervisory signal to the tolloperator at exchange A, as will be described presently. f

Relay 539 is equipped with a weighted spring armature 542 and a short interval of time required for this armature to come to rest against its working Contact after relay 539 has been energized. Relay 556, which operated in the abovetraced circuit upon the operation of relay 551, at armature 557 closes lone point in the shunt circuit of relay 551, at armatures 560 and 561 it opens the trunk to the toll board in exchange B, and at armatures 558 and 559 it connects ringing generator and ground to the outgoing line conductors. This ringing current is transmitted over wipers 588 and 591 and the associated bank contacts, conductors 40 and 43, conductors '774 and 775, to the toll transmission selector S2 and serves to start the automatic ringing of the called line by the toll connectorV switch, as is fully disclosed in the above-mentioned patent to Tharp.

The splash of generator current which is transmitted to the toll transmission selector by the operation of relay 556 is terminated upon the release of relay 551 after the weighted spring armature 542 of relay 539 has come to rest and completed a shunting circuit for the upper winding of relay 551 extending from ground at the working contact of armature 587, armature 557 and its working contact, armature 543 and its working contact, weighted spring armature 542 and its working contact, to the lower terminal of the upper wind ing of relay 551. The resistance is provided to prevent the Shortircuiting of the battery. When` relay 551 releases it closes a point in the talking circuit at armature 555 and its resting contact, at armature 554 and its working contact it opens the initial energizing circuit of relay 539, and at armatures 552 and 553 it opens points in the operating circuit of relays 556 and 551.

Returning now to the pointv where relay 539 operated and at armature 540 completed a circuit from ground on the hold conductor 333 to conductor 34 to operate relay 616 in the repeater R2, the two windings of relay 618 are energized in series and the relay begins to operate. However, as soon as armature 622 closes its working contact, a circuit is completed from ground at the working contact of armature 648 and said armature, armature 622 and its working contact,

obvious circuit for relay 633. As soon as relay 625 v operates it opens the shunting circuit to the lower winding of relay 618 and allows this relay to operate completely. At armature 623 and its resting contact, the initial energizing circuit of relay 625 is opened but this relay is now locked to ground at armature 628 and its working contact. At armature 615 and its working contact, relay 618 connects the frequency control lead 24 to conductor 670 over which alternating current of frequency F3 is supplied. Relay 625, in operating, at armature 626 and its working contact connects ground to conductor 23, through the winding of relay 406 of tone group 73242, to battery. The operation of relay 406 completes the circuit of relay 400 in an obvious circuit, and at armature 403 and its working contact it connects the plate circuit of the sending tube 410 to the frequency control conductor 24 which is extended over armature 637 and its resting contact, armature 619 and its working contact, armature 603 and its working contact, to

lead 670 over which current of frequency F3 is transmitted. The operation of relay 400 connects the secondary winding of output transformer 419 across the outgoing trunk conductors 20 and 21 to transmit the supervisory signal to exchange A to indicate to the operator that the called line has been seized. l

As was previously explained, the basic signalling current of one thousand cycles per second is interrupted at several different low frequencies for the transmission of the different supervisory signals. Four frequency leads have been indicated as extending to the voice frequency dialling repeaters, such as R1 and R2. The source of these different frequency currents may be the regular ringing converters which are used for frequency ringingin the automatic telephone exchanges.

Thus the frequencies may conveniently be as follows: frequency Ell-thirty cycles per second; fre- Returning now to the point where relay 400 operated and connected the secondary winding of transformer 419 across the outgoing trunk conductors 20 and 2l, alternating current of one thousand cycles per second, interrupted at a frequency of nity-four cycles per second, which has been assumed for frequency F3, is transmit# ted over the trunk 4line comprising conductorsj 20 and 21 to the automatic exchange A. The duration of this supervisory signal is determined by the time required for the weighted spring engaged by armature 634 to come to rest and complete a shunting circuit for relay 625. When armature 634 finally maintains its contact closed, relay 625 is shunted in a circuit extending from ground at the working contact of armature 607 and said armature, armature 634 and its working contact, to the upper terminal of the winding of relay 625. Relay 625 accordingly releases and armature 627 and its working contact opens the circuit of relay 633 and allows this relay to release. At armature 626 and its working contact it opens the circuit of relay 406 which accordingly releases, and at armature 407 and its working Contact opens the circuit of relay 400. Relay 400 in releasing disconnects the sending apparatus from the outgoing trunk line and at the resting contacts ofV armatures 401 and 405 it again extends the trunk conductors to the toll selector TS2.

The one thousandcycle signalling currentinterrupted at frequency F3 or fifty-four cycles per second, is received at the tone group TG1 in eX- change A and passes through the primary winding of input transformer 326. The current induced in the secondary winding of this transformer is impressed upon the grid of tube 310 causing a corresponding plate current through the primary winding of transformer 319. The current induced in the secondaryv winding passes through the thousand cycle tuned reed relay 322 and causes this relay to open contacts 324 at the rate of fifty-four times per second. The opening of contacts 324 at the frequency F3 interrupts the circuitY of tuned reed relays 254 and 266 at a corresponding rate. The tuned reed 255 of relay 254 is designed to vibrate at fiftyfour cycles per second, and when the circuit of relay 254 is interrupted at this ratethe reed begins to vibrate and operates the armatsure spring 256, thereby opening the circuit of relay 252. Relay 252 releases and at armature 253 and its resting contact completes an obvious circuit for relay 257.

Relay 257 operates and at armature 258` and its working Contact locks itself operated to ground at armature 2620i relay 260 through armature 211 and its Working contact. At armature 259 and its working contact it connects ground to conductor 3 which is extended over this conductor to the winding of relay 163 of toll selector TS1. Relay 163 operates and atrarmatures 165 and 166 and their working contacts connects the battery-feed coil 162 across the two line conductors extending to the toll board in exchange A. This battery connection to the line conductors operates the supervisory relay in the cord circuit CCl, which corresponds to relay 761 of the cord circuit CO2, shown in Fig. l of the draw-i ings, and the latter relay at its armature and Working Contact lights the supervisory larnp associated with cord circuit CCl to inform the operator that the connection has been extended to an idle line.

As was previously explained, when relay 539 of toll selector TS2 in exchange B irst operated, it grounded the supervisory conductor 34 to transmit a supervisory signal to the toll board of exchange A and also brought about the release of relays 551 and 556 to end the splash of generator to the toll transmission selector S2 which started the automatic ringing of the connector C2. When the called subscriber answers the call, battery is removed from the conductors 774 and '175 extending to the toll transmission selector and the trunkis cut dry in a manner clearly pointed out in the above-mentioned patent to Tharp. As soon as battery is removed from line conductors 46 and 43, relay v544 in toll selector TS2 releases and at armature 545 and its working contact removes ground from the supervisory lead 34, thereby opening the circuit of relay 618. Relay 618 starts to release and its second-step armatures 619, 620, 621, and 623 close their resting contacts before the rst-step armatures 622 and 624 have opened their working contacts. When the relay reaches its first-step position, the following circuit is closed for the upper winding of the relayz'frorn ground at the normally operated contact of relay 646, armature 648, armature 622 and its working contact, armature 629 and its resting contact, resting contact of armature 626 and said armature, upper winding of relay 618,'to battery. Theenergiaation of the upper winding of relay 613 is suliicient to hold the relay in its first-step position.

.A circuit is now closed from ground at armature 648 of relay 1646, armature 622and its working contact, armature 623 and its resting contact,

Winding of relay 625, to battery. Relay 625 operates and at armature 628 and its working contact completes a locking circuit for itself .l At armature 627 and its working contact it completes a circuit for relay 633, at armature 629 and its resting contact it opens the circuit for the upper winding of relay 618 which now completely releases, and at armature 626 and its working contact it connects ground to the sending conductor 23 to operate relay 466 of *he tone group Relay 466 brings 'about the operation of relay 406 to connect the tone generating circuit to the outgoing trunk conductors 26 and 2l and at armature 463 and its working contact it connects the plate circuit of sending tube 410 to the frequency control conductor 24. Since relay 618 is now completely released, the frequency conductor 24 extends over armature 637 and its resting contact, armature 619 and its resting contact, armature 602 and its Working contact, and over conductor 663 to the source of current of frequency F4"which has been assumed to be sixty-sir; cycles per second. A signal consisting of one thousand cycle current interrupted at sixty-six cycles per second is now being transmitted over trunk line conductors 2D and 21 to exchange A.

ARelay 633 energizes when its circuit is closed atarrnature 627 of relay 625 and, after an interval, armature 634 and its working contact re.-

closed, thereby short-circuiting the winding or" relay 625 in the manner previously described. Ptelay 625 thereupon releases and at armature and its Working contact it removes ground from the sending conductor 23 to terminate the supervisory signal being transmitted over the trunk line. At armature 628 and its Working contact lit opens its own locking circuit, at armature 629 and its working contact it opens a point in the locking circuit of relay 618, at armature 636 and its working contact it opens one ground connection to the busy conductor 29, and at'arrnature 631 and its resting contact it again prepares-the initial energizing circuit of relay 618.

The answering supervisory signal transmitted over trunk line Vconductors 26 and 21'to exchange A is received at tone group TG1 and operates the thousand cycle tuned reed relay 322. Accordingly, the circuit of tuned reed relays 254 and 256 are interrupted at a rate of sixty-'six cycles per second. The reed 261 of relay 260 is tuned to respond to this frequency, and, accordingly, operates its armature 262, thereby opening the lock.- ing circuit of relay 257. Relay 25'? releases and at armature 258 and its working contact opens a point` in its locking circuit,:and at armature 259 andits working contact removes ground from the supervisory lead 3, therebyopening the circuit of relay 163 0I" toll'selector TS1. Relay 163 releases and at armatures 165 and 166 and-their working contacts removes the battery connections from the trunk line conductor extending to toll board thereby allowing the supervisory relay in cord circuit C01 to release and put out the supervisory larnp. This informs the operator that the called subscriber has answered and she may now out through. the connection'through her cord circuit and the calling and called subscribers may converse.

At the end of the conversation when the subscriber at substation T2 replaces his receiver, battery and ground are again connected to conductors '774 and 775 and. extended over conductors 40 and 43 and wipers and 591 of toll selector TS2 to again operate relay '544. Relay 544 at armature`5-45 and its working contact again connects ground to the supervisory lead 34, thereby operating relay 613 in the manner previously described. Relay 618 operates in itsA step and brings about the operation of relays 625 and 633 in the manner previously described. Relay 625 starts the transmission of a disconnect signal oonsisting or thousand-cycle current interrupted at circuit of relay 252 which releases and at armature 253 and itsresting contact completes the circuit of relay 257. Relay 25'? operates and at armature 258 and its Working contact completes a locking circuit for itself and at armature 259 and its working contact grounds the supervisory lead 3, thereby operating relay .163 of the toll selector TS1. Relay 162 again bridges the batteryfeed coil 162 across the trunk line conductors extending to the toll board, thereby lighting the supervisory lamp associated with cord circuit CCl in the manner previously described.

In case the toll operator at exchange A Wishes to re-ring the subscriber T2, she operates the ringing key associated with her cord circuit, thereby connecting ringing current over 'the tip and ring of cord circuit CCl and jack. Jl, through condenser 146, Winding of relay 144, and the retard coil 150. Relay 144 operates and at armature 145 and its Working contact connects ground from the busy conductor 2 over resting contacts of armature 107 and said armature, armature 145 and its Working contact, armature 108 and its resting contact, conductor 5, winding oi relay to battery. Relay 236 operates and at armature 237 and its working contact connects the frequency control conductor X to conductor 271, over which alternating current oi frequency F1 or thirty cycles per second is supplied. At armature 223 and its 'Working contact it connects ground to conductor Y, thereby operating relays 306 and S00 in tone group TG1. The operation oi relay 305 brings about the connection ci the tone generating equipment to the outgoing line conductors 2G and 21 and a re-ring signal consisting of thousand-cycle alternating current interrupted at thirty cycles per second is transmitted over trunk line conductors 20 and 2l to automatic exchange B.

This re-ring signal is received by tone group TG2, causing the operation of the tuned-reed relay 422, which interrupts its contacts 424 at the rate of thirty times per second. The reed 644 of tuned reed relay 643 is tuned to espond to this frequency and operates its armature 645, thereby opening the circuit of relay 64.. Relay 641 releases and at armature 642 and its resting contact connects ground to conductor 3i, thereby completing the energizing circuit for the upper Winding of relay 556. Relay 556 operates and at armatures 559 and 558 and their-Working contacts it again connects the generator leads to Wipers 588 and 591, thereby transmitting ringing current to the toll transmission selector S2. This brings about the signalling of the subscriber at substation T2 by the toll connector C2 in the manner clearly described in the above-rnentioned patent to Tharp.

The re-ring signal is transmitted over the trunk". line to exchange B as long as the toll operator at exchange A holds her key depressed. When she releases the key, relay 144 releases and at armature 145 and its Working contact opens the circuit of relay 236. Relay 236 releases and at armature 238 and its Working contact disconnects ground from conductor Y, thereby terminating vthe re-ring signal. When the called. subscriber answers after being re-rung in the abovedescribed manner, battery is disconnected from the trunk line conductors 774 775, thereby bringing about the release oi relay 544. Re lay 544 at armature 545 and its Working contact disconnects ground from conductor 24, thereby bringing about the release of relay 61S and the transmission of an answering signal to exchange A in the manner previously described. This an swering signal extinguishes the supervisory lamp at the toll operators position in exchange A,

thereby informing the operator that the subscriber substation has again answered.

l `Returning new to the point Where the superlarnp at the toll operators position in exchange A was lighted responsive Yto the discon nection of the'called subscriber, the operator now removes the plug P1 from the jack Jl. Relay releases and removes ground from the hold conductor l, thereby opening the circuit oirelay 212 of voice frequency repeater R1. Relay 212 releases and -at armature 213 and its Working Contact disconnects ground from conductor '265 and connects this conductor tothe impulse conductor Z. At armature 214 and its Working contact it opens the locking circuit of relay 218, at arrnatrre and its Working contact it removes the ground shunt from armature 235 of relay 233 and the associated Weighted spring contact, at armature 22.6 and its Working contact it removes ground trom the busy conductor 2, and at armature 23.7 and its Working contact it opens a point in 'the locizing circuit of relay 257.

2l8 begins to release and as soon as armature closes its resting contact a circuit is closed from ground at the Working Contact of arma-'tine .s and said armature, armature 222 and i Working contact, armature 229V and its rest g contact, resting contact of armature 220 nature, upper Winding of relay 213, to Y .ne energization. ci the upper Windoi the relay is sufiicient to hold the relay in its first step with armatures 222 and 224 still operated., but the remaining armatures in engagement with their resting contacts. A circuit therefore, closed from ground at armature 248, ature 222 audits working contact, ar-Y mature 223 and its resting contact, Winding of relay to battery.

Relay energizes at armature 227 and its Working contact completes a circuit for the timing relay 233. armature 229 and its reste contact it opens the circuit for the upper t) winding of relay 23.8 ard allows this relay' to conipletely release. at a" ature 226 its Working contact it connects ground the sending conductor Y, thereby operatingrrelay ci tone group TG1. Relay 356 in turn operates the re lay 32C, thereby connecting the tone generating circuit to trunk conduct 2G At armature and its Wer. g contact, relay connects the pl e clcuitoi sending tube' to conductor 2 which extends over mature 227 and its Yresting contact e" resting contact, armature .mature 219 as three times as ong the itor arrcature 234 to niaintain contact with its Weighted spring ar mature.

and rest-V ing contact, to frequency conductor A?? second is L 5 ci relay 233 its conf? When armature 235 finally completes its con- Working contact, to the upper terminal of the going trunk conductors.

winding of relay 225. Relay 225, therefore, releases and at armature 226 and its working contact disconnects ground from the sending conductor Y, thereby terminating the release signal. At armature 228 and its working contact it opens its own locking circuit, at armature 227 and its working contact it opens the circuit of relay at armature 231 'and its resting contact it again prepares a circuit for relay 218, and at armature 230 and its working contact it disconnects the last ground connection to the busy conductor 2.

Ground has now been removed from the hold conductor 1 and the busy conductor 2 and relay 167 in toll selector TS1 accordingly releases. The equipment in the automatic exchange A has now been restored to its normal condition.`

The long release signal consisting of one 'thousand cycle current interrupted at a rate of fortytwo times per second is received by tone group TG2 and operates the tuned reed relay 422 which in turn opens the circuit of relays 643, 649, and 663 at a corresponding rate. Relay 649 responds to this signal and its vibrating armature 656 operates armature 651, thereby opening the circuit of relay 646. Relay 646 releases and at armature 647 and its working contact opens a point in the impulsing circuit and at armature 648 and its working contact it opens the locking circuit of relay 600 which accordingly releases. Relay 600, in releasing, at armature 604 and its working contact opens a point in the circuit of the polarizing winding of relay 639, at armature 669 removes ground from the busy conductor 29, and at armature 616 and its working contact removes ground from the hold conductor 33.

The removal of ground from hold conductor 33 brings about the release of relay 500. Relay 500, in releasing, at armature 509 and its working contact opens the locking circuit of relays 539, 547, and 512. At armature 510 and its resting contact it completes the circuit for release magnet 534 vover oi-normal'springs 528, and the toll selector TS2 accordingly releases. The removal of ground at armature 569 and itsworking contact also opens theloclring circuit of relay 531 which releases and in turn opens the circuit of relay 567. The selector TS2v and its associated repeater and tone relay group have now restored to normal. y

The releaseof the toll selector TS2 removes ground from. the control conductor 42 extending to the trunk. kvcircuit TG2, thereby allowing relay 746 to release. At armature 746 and its working contact relay 746 opens the circuit of relay 749, and at armature 747 and its working contact it opens a point in the bridge circuit across the out- Relay 749 releases and at armature 752 and its 'working contact opens the locking circuit of relay 754, at armature 750 and its workingr contact removes ground from the test conductor 4l, and at armature 753 and its resting contact closes a loop circuit-across 'the outgoing trunk conductors 774 and 775 through relay 771. Sincebatteryis connected across these trunk conductors at the toll transmission .selector, relay 771 operates and at armature 772 and its working contact opens the locking circuit of relay 760. Relay 760 releases and at armature 762 and its working contact it removes the last ground connection from the test conductor 41, thereby rendering this trunk circuit. available to selectors, at armatures 761 and 766l it removesV the short-circuit from condensers 767 and 768,

' and at armature 765 and its working contact it opens the bridge circuit including relay 771. After an interval relay 771 releases andv again prepares the locking circuit of relay 760.

As the loop circuit to the toll transmission selector. S2 and connector C2 has now been opened, these switches release in the manner clearly described in the above-mentioned patent to Tharp. All thel apparatus used in the establishment of a connection from the toll operator at exchange A to substation T2 in exchange B has now been released and is in its normal condition.

In case the operator at the toll board A is the iirst to release, the voice frequency repeater R1 and the one group TG1 transmit the release signal over conductors 20 and 2l to exchange B in the manner pointed out above. This brings about the release of the toll selector TS2, thereby removing ground from the control conductor 42 extending to trunk circuit TG2. Relays 746 and 749 are accordingly released in the manner pointed out above and the relay 771 is bridged across trunk conductors 774 and 775 extending` to the toll transmission selector S2. Relay 760 remains locked energized to the back contacts of armature 772 and at armature 762 and its working .contact maintains ground on test conductor 4l to prevent the seizure of the trunk circuit TG2 by any selector, such as TS2. When the called party replaces his receiver, battery is connected to trunk conductors 774 and 775 and relay 771 operates to open the looking circuit of relay 760 in the manner previously described. Relay 760 releases and at armature 765 opens the circuit of relay 771, thereby allowing this relay to release. Thus it isseen that the release of the toll train is controlled by the last party to disconnect. Y

In the foregoing explanation of the establishment of a call from the toll operator at exchange A to a substation such as T2 in exchange B, the utility and function of relay 639 in the Voice frequency dialling repeater R2 was omitted for clarity. The purpose and operation of this relay will now be explained.

Referring to Fig. 6 of the drawings, it is seen that when ground is intermittently removed from the receiving conductor 22 responsive to the receipt of dialling impulses or thousand-cycle signalling current interrupted at frequencies F1 or F2, the circuits of the tuned reed relays 643 and 649 and of the lower winding of relay 663 are intermittently interrupted. Relay 663 controls the operation of the toll selector TS2 and succeeding switches in the toll train by connecting ground to the impulse conductor at armature 664 and its resting contact responsive to thousand cycle current interrupted at dial speed. However, when a signalling current is received interrupted at frequencies F1 or F2 the circuit of relay 663 is also interrupted and armature 664 wouldordinarily be released to send ground impulses over the impulsing conductor 35, thereby interfering with the operation of the switches and causing chattering of relays during the time that the switches are in talking condition. Also, in case the toll operator wishes to release the connection after it has been partially set up, the release signal consisting of thousand cycle current interruptedl at frequency F2 would intermittently release relay 663, thereby sending impulses over the impulsing lead to the automatic switches. The operation of the repeating relay 746 of the trunk circuit TG2 causes a short-circuit to be placed across the trunk conductor 

